1. Field of the Invention
The present invention relates to electrical multi-pin plug connections and, more particularly, to multi-pin male and female contact bars which are adapted for the connection of multi-conductor flat ribbon cables to a printed circuit board or to other cables. It also relates to a method of manufacturing and assembling composite contact posts for such multi-pin contact bars.
2. Description of the Prior Art
The rapid growth in the use and transmission of electronic data and signals, in conjunction with the advantages which can be realized through structural modularity and the application of the building block principle to the electronic controls of complex production machines, for example, has created a need for multi-conductor plug connections in the form of compact, standardized male and female contact bars forming large numbers of contacts for the pluggable connection of wire harnesses to printed circuit boards and for wire harness couplings.
In order to achieve very closely spaced contact positions, and with the aim of establishing reliable solder-free electrical connections between the metallic contact members and the conductor strands of a multi-conductor cable, it has already been suggested to produce the numerous closely spaced electrical connections by means of a contact blade configuration in which each contact post terminates in a yoke-shaped contact blade with a central slot by means of which the contact member engages the conductor strand. The forcible engagement of the contact blade over a conductor causes the contact blade to locally penetrate and displace the insulating sheath surrounding the conductor strand and to firmly wedge the strand wire between the flanks of the blade slot.
The German Offenlegungsschrift (Published Application) No. 27 47 264 discloses a multi-conductor contact bar which holds a row of female contact posts with two conductor penetrating blades guided in a plastic housing. The connection of such a contact bar to a printed circuit board necessitates the use of a special intermediate pin bar with pins having one extremity attached to the solder sockets of the printed circuit board and the other extremity engaged by the female contact posts of the contact bar.
The contact posts of this prior art contact bar are arranged in a single row and symmetrical with respect to both the longitudinal axis and a plane which is perpendicular to that axis. The smallest pitch of the conductor strands in a ribbon cable attached to this contact bar is equal to the longitudinal distance between two contact posts in the plastic contact bar housing.
These prior art contact posts have two parallel blade tines linked by a transverse web portion in the center of which is arranged a socket opening for the insertion of a contact pin. A long slot which extends from the socket opening into the blade tines gives the contact post a limited degree of flexibility.
The structure of these contact posts lends itself to the mechanized die-cutting of the contact posts from a continuous strip of sheet metal which can be surface-treated and stored as a coil of semi-finished contact post segments. However, the assembly of these contact posts into a contact bar requires a complex automatic assembly machine which must first bend the contact post segments from a flat shape into the shape of a "U", then sever them from the sheet metal segment strip in a cutting action, and finally insert the contact posts into the contact bar housing.
The electrical connections between the contact blades of the contact posts and the conductor strands of the ribbon cable are established in the process of inserting the contact posts into the contact bar housing. Accordingly, it is not possible to attach such a contact bar to a ribbon cable in the field, where the special assembly machine is not available.
From the German Offenlegungsschrift No. 27 24 244, which corresponds to U.S. Pat. No. 4,068,912, it is known to arrange two adjacent rows of contact members in a common contact bar housing with a longitudinal offset between the two rows which is equal to one-half of the contact member pitch. Such a contact bar is connectable to a ribbon cable with conductor strands spaced at one-half the pitch of the contact members.
This prior art solution, while lending itself to the use with ribbon cables of very small pitch, has the shortcoming of having only one contact blade for each conductor strand, with the additional disadvantage of using the contact posts themselves as locking elements for the attachment of the cable clamping member to the contact bar housing.
This locking action is obtained by forcing each contact blade through a tapered slot in the cable clamping member, thereby causing the two lobes of the blade to be deflected towards each other. Only after the contact blade has been fully inserted, are the blade lobes allowed to spring back to their normal spacing, their latching protrusions thereby becoming engaged behind interior supporting shoulders of the housing.
It follows that, as the contact blades penetrate the conductor sheath to wedge their slot flanks against the conductor strands, the slots are, in effect, narrower than in the fully inserted position of the contact posts, with the result that the metal-to-metal contact pressure between the contact blades and the conductor strands is relaxed, rather than maintained or increased, as the blades snap into their locking positions.
Also known from the prior art is a composite female contact post which consists of a contact portion in the form of a pair of spring tines connected together by a bridge portion and a solder pin which is welded to that bridge portion. The bridge portion adjoins the spring tines at their longitudinal edges, thus forming a wall portion which extends parallel to the center axis of the contact post and parallel to the longitudinal axis of the solder pin. The solder pin is spot-welded to the inner side of this bridge wall portion.
Past attempts at obtaining a butt-welded connection between a contact member and a pin have met with failure, due to the small area of the resistive interface at the extremity of the pins and the resultant difficulty of obtaining a consistent heat input that would prevent mere adhesion on one extreme and burn-off on the other extreme.
Another reason why it has been impossible in the past to obtain reliable butt-weld connections for the pins is related to the fact that different metal alloys are used for the two component parts of the contact posts: brass for the upper contact post portions which undergo bending in production and which must provide a spring response, in the case of the female contact members, and contact bronze for the solder pins and plug pins.